Spatial Distribution and Number Density of Scatterers in the Upper Uranian Atmosphere

C. M. Walter, M. S. Marley (NMSU), H. B. Hammel (MIT)

Since the visit by Voyager 2 in 1986 the amount of haze in the
stratosphere and upper troposphere of Uranus has increased by an order
of magnitude. The full disk albedo of the planet in narrowband
near-infrared images of the planet taken at Apache Point Observatory
from August 1995 to October 1996 is larger than can be accounter for
by the Voyager haze. In an effort to confirm this and
determine the spatial distribution of the haze we have examined high
resolution images (FWHM = 0.3-0.5 ) taken at the IRTF
in Mauna Kea, HI in late August 1995.

The data was modeled by using center-to-limb fits of the photometric
quantity I/F along specified
latitudes. The model I/F values were computed using a multi-layer
adding-doubling code. Our dataset consisted of several images in a
broadband K filter spread over six nights. The K filter is
particularly useful because it encompasses strong CH and H
absorption bands, making this filter highly sensitive to the
atmosphere above the CH cloud. At these wavelengths the
contribution to the reflected light by Rayleigh scattering
is smaller than the component from scattering by the haze, which
allows its effect to be effectively isolated and measured.
Preliminary results confirm the order of magnitude increase, and show
that the distribution of haze is uniform across the disk.